Petroleum pitches are recognized as suitable sources of carbon and, if having the proper softening point, can be used satisfactorily as an impregnation material for electrodes, anodes, and carbon-carbon composites, e.g., carbon-carbon fiber composites, such as aircraft brakes and rocket engine nozzles. The pitches can be used in the nuclear industry for the preparation of fuel sticks for a graphite moderated reactor. Furthermore, such pitches can be used in the production of carbon fiber precursors, carbon fibers, and graphite fibers.
Carbon and graphite fibers provide a high strength per weight ratio. Such property enables them and composites made from them to be used in sporting equipment, automobile parts, light-weight aircraft, and increasing aerospace applications.
While various different carbonaceous materials (sometimes called fiber precursors) have been disclosed in the prior art for the manufacture of carbon or graphite fibers, two significant commercial processes employ polyacrylonitrile or mesophase pitch to produce high-strength graphite fibers. However, such processes have disadvantages. For example, the preparation of mesophase pitch requires that the initial feedstock be heated to an elevated temperature for a number of hours, as shown by Lewis, et al., in U.S. Pat. No. 3,967,729, by Singer, in U.S. Pat. No. 4,005,183, and by Schulz, in U.S. Pat. No. 4,014,725. Therefore, such a process is time consuming and costly. In addition, care must be taken in heating for a specific time, since mesophase pitch can increase in viscosity rapidly, making it unsuitable for spinning. On the other hand, polyacrylonitrile is a relatively expensive feedstock, equalizing the overall cost of producing fibers from polyacrylonitrile with the cost of producing carbon or graphite fibers from mesophase pitch.
Recently, Sawran, et al., in U.S. Pat. No. 4,497,789, have disclosed a process for producing substantially non-mesophasic pitch and a method for producing carbon fibers therefrom. The disclosure of this patent is expressly incorporated by reference herein and made a part hereof.
Now an improved process for the manufacture of pitches having relatively high softening points has been developed. In addition, an improved process for making carbon fiber precursors, as well as carbon fibers, has been developed. In these improved processes, an elevated wiped-film evaporator is employed.